Veos obtains a treasure scroll that directed him to potential treasure somewhere around Lumbridge. However, as he has never travelled in this area before, he does not know how to complete the scroll. The player offers to help him complete the scroll, upon which they found an ancient casket, which led to them hearing a faint whispering.

Regardless, they deliver the casket to him. When asked about the contents of the casket, Veos will reply shiftily, saying "Oh err... Nothing important. Just something that might be of use to me back in Great Kourend."

Veos enlists the player's assistance to gather knowledge on the current state of Great Kourend's hierarchy and general social organisation for a client. After visiting the five cities of Great Kourend, the client requested the player to activate a mysterious orb near the Dark Altar.

The player soon discovers that Veos does not recall any of the prior events, and he becomes possessed by the client, claiming that Veos is of good use to him as a conduit before making his grand entrance. When asked for his name, he will refuse, stating that all will be revealed in time.

The gangs of Great Kourend have been uniting under a mysterious figure called the Queen of Thieves, and Tomas Lawry is assigned to investigate this on behalf of the Kourend Council, the ruling power of Great Kourend.

Thomas enlists the player's help in infiltrating the Saviours of Kourend, the gang that has absorbed many of the other gangs within Kourend. The player eventually discovers the hideout of the gang in The Warrens, and kills Conrad King, a senior member of a rival gang, the Vipers, in order to gain the trust of Devan Rutter.

After gaining his trust, Devan allows the player to gain an audience with their leader, the Queen of Thieves. She reveals herself as Lady Shauna Piscarilius, the leader of Piscarilius. She tells the player about the corrupt leadership of the Kourend Council, and asks that they search the house of Sophia Hughes, one of the four members of the Council. The player then discovers that she has ties with the Disciples of Yama, a Zamorakian cult, proving Shauna's claims.

Upon returning to Thomas with this evidence, he promptly abandons his investigation and reports this to the Council, who have her arrested and locked up in the jail cells on the top floor of Kourend Castle.

After speaking to their chef, Olivia, it is revealed that Artur was searching for the Royal Accord of Twill, a document of historical significance, and had been spending most of his time in the Arceuus Library. There, the player finds a book that may lead to the whereabouts of the Accord, and therefore Artur. After navigating the Crabclaw Caves, the player finds Artur, and a chest containing the Accord.

As the player returns to Kandur, he will decide to keep the Accord for safekeeping and to use it as a leverage should the other Houses of Kourend cause him trouble.

However, he received a parcel from an unknown individual containing an old journal written by King Shayzien VII, with a note on the parcel claiming the journal was stolen from the Tower of Magic during the uprising against Xeric in the 47th decade. Although most of the journal is illegible, he managed to find an extract stating "Quidamortem's creatures are compatible. The experimentation is proving successful and we will soon be ready to mass produce."

The extract had a date in the 37th decade, and yet the expedition was declared a failure a decade before, leading Phileas to question why the king wrote about Quidamortem a decade after the failure of the expedition. He will ask the player to discover the truth about his ancestor's expedition by visiting the Library Historical Archive. Here, the player discovers evidence that the journal may be genuine, and is prompted by Phileas to perform the expedition once more. The player is granted permission to go on the expedition by Lord Shiro Shayzien, who asks that any discoveries made be brought to him first, as King Shayzien VII was his ancestor and he wants to be made aware of any discoveries that may present him in a bad light.

Upon arriving at the summit of the mountain, an expedition from the Varrock Museum reveals that they have uncovered a small cave. The player discovers a temple with an unstable altar, and brings the Museum expedition to investigate. The cave is revealed to have predated Xeric, and he may have used this altar to extend his lifespan during his exile, suggesting that he may still be alive.

Upon returning to Lord Shiro Shayzien, he asks for proof of the player's discoveries, and prompts the player to visit Phileas for the journal. However, players discover that his tent has been trashed and he himself has gone missing. Shiro will then open an investigation into his disappearance. Without the parcel, no concrete evidence can be linked to King Shayzien VII and the player's discoveries, but he will contact the research team and ensure they are documented.

Undor has discovered the cause of the failure of the Doors of Dinh, and sends a report to Councillor Unkar, a member of the Kourend Council, to request for assistance. The Doors of Dinh were created by the master blacksmith Dinh to imprison the Wintertodt, an unknown entity which brings with it extremely freezing temperatures. The Wintertodt had previously ravaged Great Kourend 1,400 years ago, and it was only with Dinh and the Order of the Sacred Flame's help that the Wintertodt was sealed in its prison. With the doors failing, there is no telling what havoc the Wintertodt can wreak if it breaks free.

The player meets with Unkar at the Wintertodt Camp, where he will explain that the Doors have been purposely damaged by someone or something, creating a small hole in the doors. Although not much, it is enough for the Wintertodt imprisoned within to draw a small amount of power into the prison. He can repair the damage, but he requires Dinh's hammer, located in The Forsaken Tower.

The player travels to the Forsaken Tower to find Dinh's hammer, which is being safeguarded by multiple puzzles. They solve the ancient puzzles and eventually retrieve Dinh's hammer and return to Unkar, who repairs the damage. Despite the player's efforts, the Wintertodt manages to obtain a significant amount of power and now it is up to the Order's pyromancers to subdue it.

Mori is walking to the Arceuus Library with her friend Thana when they felt a strange power flow through them. Suddenly, Thana inexplicably dies without warning. Since the Ascent of Arceuus, an event over a thousand years ago which allowed all of Arceuus to become immortal, no member has died of natural causes. Mori catches the player passing by and tells them to inform the Kourend Council. However, they are unable to lend their assistance, as the Arceuus have chosen to keep their knowledge secretive. Frustrated, Mori then asks the adventurer to inform Lord Arceuus, as he cannot ignore the death of one of his people.

The player visits the Tower of Magic and informs the Tower Mages outside of Thana's death, which they believe may be linked to the problem they are facing inside. Inside the tower, several souls have become violent and began to attack the mages, who the player slays with ease. Upon clearing the floor of the tormented souls, they meet with Lord Arceuus' son, Asteros Arceuus and informs him of Thana's death.

Asteros informs the player their instruments detected fluctuations in the power of the Dark Altar, causing them to feel a strange loss of power, as if the Altar itself had failed altogether. After realising this, Lord Arceuus used himself as a conduit to channel what little power the Dark Altar had left. This failure of the Dark Altar is what caused the experimental trapped souls to break free and turn feral, and caused Thana's death. Lord Arceuus' power is the only thing keeping his people alive. He then asks them to visit the Tasakaal, as they were the ones who gave his father the secrets of immortality.

The player heads to Mount Karuulm to visit the Tasakaal, who initially refuse to help them after hearing of Arceuus' plight. However, after some convincing by the adventurer, they agree to help if the player tracks down a trapped soul. The player tracks and frees the soul from its torment, fulfilling their end of the deal. The Tasakaal also fulfill their end and inform the player that someone had placed a device to redirect the Dark Altar's power. The adventurer finds the device near the Dark Altar, and destroys it.

With the device destroyed, Lord Arceuus snaps out of his magical trance. The player informs him of the device they destroyed, and he sends researchers to investigate the broken device. Lord Arceuus is concerned that someone would deliberately try to sabotage the Dark Altar, but nonetheless thanks the player for saving his people.